With the development of society, the occurrence of occupational diseases is on the rise. Conventional office desks are constant in height; or, their height may be customized during manufacturing, but it is difficult to change the height once they are delivered. Office workers are very easy to have occupational diseases at their waist, back, neck or legs if they work on an office desk at the same height for a long period of time. Since such occupational diseases resulted from long-time sitting have troubled many workers, standing office or alternate sitting and standing office first becomes popular abroad. This office style has various advantages. Particularly, this office style may avoid the occurrence of some lumber and cervical spondylosis and also has a certain effect of losing weight. Research reports have indicated that this office style may also improve the working efficiency by 10% to 30%.
Due to the problem of inappropriate desktop height resulted from the change between the standing office and the sitting office, various height-adjustable desktop products have been provided. Chinese Patent Publication CN102715729B has disclosed a lifting desktop, wherein two support legs are in transmission connection to one another successively by a motor, a speed reducer and a screw so that the desktop is lifted electrically. With this technical solution, the lifting desktop is very compact in a folded state and will not influence the normal use of the original desk when it is placed on the desk. The height to be adjusted is freely selected by electrically or manually driving the screw, and it is thus convenient to change between the standing office and the sitting office. However, this technical solution has the disadvantage of low speed in lifting the desktop, due to the driving by the screw. Moreover, electrical driving is costly, whereas manually shaking the screw requires good physical fitness of a user.
U.S. Pat. No. 9,504,316B1 has disclosed a height adjustable desktop assembly. The technical solution of this patent includes a desktop support, a base frame, support frames which are provided between the desk support and the base frame and pivoted to each other in an X-shaped form, and hydraulic cylinders connected to the base frame and a position close to a middle portion of one support leg of the support frames. The technical solution of this U.S. patent also has various disadvantages: firstly, when the desktop is actuated from a folded state, the hydraulic cylinders provide limited assistance in lifting the desktop since they are approximately horizontally arranged, and additionally, it is difficult to manually lift the desktop due to the weight of objects on the desktop; and secondly, since it is difficult to completely unfold the desktop due to the presence of the central pivot in the middle of the X-shaped support frames, the structure is not compact and the normal use of the original desk is influenced. As far as the present applicant knew, European Patent Publication No. EP0937677A2 has disclosed scissor lifts. The lift includes two support legs crossing each other, wherein each of the support legs is provided with a roll end and a fixed pivot end; a connecting rod is pivoted onto one of the support legs; one end of the connecting robe is provided with a roller and resisted against the other support leg, while the other end thereof is pivoted to a piston rod; and, the other end of the piston rod is pivoted to the other support leg. In the technical solution, an upward thrust force is generated by a connecting rod under the action of the piston rod, so that an actuating assistance is provided to the lift during the actuation. However, since the piston rod is arranged between two support legs on a same side, there will be the following disadvantages: firstly, the lifting assistance to the lift is not satisfactory during the lifting process of the lift after actuation, because no sufficient torque is provided to the support legs; secondly, since the piston rod is arranged between two support legs on a same side, the maximum extension length of the piston rod is limited, and the lifting height of the lift is thus influenced; and thirdly, due to the arrangement of the connecting rod structure and the piston rod, the lift cannot be unfolded completely, resulting in poor structural compactness. Therefore, this technical solution cannot be applied to a lifting structure of a lifting desktop.